Examples of conventional sample detector are disclosed in Patent Documents 1-3 identified below. In the sample detectors disclosed in these documents, a predetermined detection area is irradiated with light from a light source, and light reflected by or transmitted through the detection area is received by a light receiving element. Based on the reflectivity or transmittance of the detection area, whether or not a sample is present in the detection area is determined. In Patent Documents 2 and 3, a pair of light sources are used to irradiate two separate regions with light. With this arrangement, it is possible to determine whether or not a sufficient amount of sample is present over two regions, so that the detector is applicable to a relatively large detection area.
In the sample detector, if light is simply directed toward the detection area, the light reaches also the portions other than the detection area, whereby light passing through the portions other than the detection area may be received by the light receiving element. In this case, erroneous determination may be made as to whether or not a sample is properly present in the detection area. Therefore, the sample detectors disclosed in Patent Documents 1-3 employ or require a means to guide the light emitted from the light source properly to the detection area by using an optical lens.
However, the use of an optical lens as described above increases the component cost. Further, the incorporation of an optical lens in a device complicates the structure of the device and hence increases the manufacturing cost of the device. Moreover, since a space for placing the optical lens is necessary, the overall device becomes large. These problems are more serious in the case where the device includes a plurality of light sources, because a plurality of optical lenses are necessary.
Patent Document 1: JP-A-2004-163393
Patent Document 2: Japanese Patent No. 3455654
Patent Document 3: U.S. Pat. No. 5,889,585